1. Field of the Invention
The invention relates to an electrochemical storage cell based on sodium and sulfur having an anode space and a cathode space, which are separated from one another by an alkali-ion-conducting solid electrolyte and defined at least partially by a metal housing.
2. Description of the Prior Art
Such electrochemical storage cells are suitable as energy sources. They are increasingly used in designing storage batteries that are intended for supplying current to electric vehicles.
One special example of these storage cells is the cells based on sodium and sulfur, which are rechargeable and have a solid electrolyte of beta-aluminum oxide, which separates the anode space from the cathode space. One pronounced advantage of these storage cells is that when they are charged, secondary electro-chemical reactions do not take place, and so the current yield is approximately 100%. In such storage cells, the anode space is filled with sodium and disposed inside the solid electrolyte. The cathode space is located between the solid electrolyte and the metal housing, which defines the storage cell with respect to the outside. Aluminum is preferably used for producing the housing. The reactants contained in the storage cell, or the reaction products that form, are highly corrosive substances. Accordingly the housing walls that come into contact with the reactants are exposed to corrosive influences. To overcome these disadvantages, it has already been proposed in the journal "Thin Solid Films" 83 (1981), page 417, that the inner surfaces of the metal housing of these storage cells be coated with an anti-corrosion film. To form this anti-corrosion film, alloys containing chromium, nickel, cobalt and molybdenum were proposed.
German Published, Non-Prosecuted Application DE-OS No. 24 57 418, discloses applying a protective film of graphite to the inner surfaces of an electrochemical storage cell.
U.S. Pat. No. 3,749,603 describes a metal housing of light metal, the inner surfaces of which are protected from corrosion with a coating of molybdenum sulfide.
The above possibilities are capable of improving the corrosion resistance of the housing for a short time, but they have the disadvantage that the internal resistance of the storage cells, with increasing age, increases very sharply because of the formation of sulfide-containing films, or other kinds of non-conductive films, on the inner wall of the housing.